1. Field of the Invention
The present invention relates to a four parallel shaft type automatic transmission comprising, in parallel, a main shaft, a counter shaft, a first sub-shaft and a second sub-shaft.
2. The Related Art
Japanese Patent Publication No. 2900201 discloses a three parallel shaft type automatic transmission for a vehicle which can establish five forward speed gear stages and one reverse gear stage.
FIG. 6 is a schematic diagram illustrating the above-mentioned three parallel shaft type automatic transmission of the art; this automatic transmission T comprises a main shaft Sm connected to an engine E via a torque converter 23, a counter shaft Sc and a secondary shaft Ss placed parallel to the main shaft Sm, and the rotation of the counter shaft Sc is transmitted to right and left driven wheels WR and WL via a differential gear box 25.
A first gear G1 and a second gear G2 are supported in a relatively rotatable manner on the main shaft Sm which is supported by means of a pair of bearings 14 and 15, and the first gear G1 and the second gear G2 are connected to the main shaft Sm via a fourth speed-reverse clutch C4R and a fifth clutch C5 respectively. The fourth speed-reverse clutch C4R and the fifth speed clutch C5 are provided back-to-back on an axially central part of the main shaft Sm. A ninth gear G9 for transmitting the forward driving force to the counter shaft Sc and the secondary shaft Ss is fixed on the main shaft Sm.
A third gear G3 and a fourth gear G4 are supported in a relatively rotatable manner on the secondary shaft Ss which is supported by means of a pair of bearings 18 and 19, and the third gear G3 and the fourth gear G4 are connected to the secondary shaft Ss via a first speed clutch C1 and a second speed clutch C2 respectively. The first speed clutch C1 and the second speed clutch C2 are provided back-to-back on an axially central part of the secondary shaft Ss. A tenth gear G10 is fixed on the secondary shaft Ss, and the forward driving force is transmitted from the main shaft Sm to the tenth gear G10.
A sixth gear G6 meshed with the second gear G2 of the main shaft Sm is fixed on the counter shaft Sc which is supported by means of a pair of bearings 16 and 17, and a seventh gear G7 and an eighth gear G8 meshed with the third gear G3 and the fourth gear G4 of the secondary shaft Ss respectively are also fixed on the counter shaft Sc. Furthermore, a fifth gear G5 meshed with the first gear G1 of the main shaft Sm is supported on the counter shaft Sc in a relatively rotatable manner, and the fifth gear G5 is connected to the counter shaft Sc via a chamfer 56. Moreover, an eleventh gear G11 meshed with both the ninth gear G9 of the main shaft Sm and the tenth gear G10 of the secondary shaft Ss is supported on the counter shaft Sc in a relatively rotatable manner, and the eleventh gear G11 is connected to the counter shaft Sc by means of a third speed clutch C3. The third speed clutch C3 is provided on the end of the counter shaft Sc opposite to the engine E.
A main reverse gear 51 formed integrally with the first gear G1 of the main shaft Sm is meshed with a counter reverse gear 54 supported on the counter shaft Sc via a reverse idler gear 55 in a relatively rotatable manner, and this counter reverse gear 54 is connected to the counter shaft Sc by means of the above-mentioned chamfer 56.
In accordance with the above-mentioned arrangement, when the first speed clutch C1 is engaged, the rotation of the main shaft Sm is transmitted to the counter shaft Sc via the ninth gear G9, the eleventh gear G11, the tenth gear G10, the secondary shaft Ss, the first speed clutch C1, the third gear G3 and the seventh gear G7 so establishing a first speed gear shift stage.
When the second speed clutch C2 is engaged, the rotation of the main shaft Sm is transmitted to the counter shaft Sc via the ninth gear G9, the eleventh gear G11, the tenth gear G10, the secondary shaft Ss, the second speed clutch C2, the fourth gear G4 and the eighth gear G8 so establishing a second speed gear shift stage.
When the third speed clutch C3 is engaged, the rotation of the main shaft Sm is transmitted to the counter shaft Sc via the ninth gear G9, the eleventh gear G11 and the third speed clutch C3 so establishing a third speed gear shift stage.
When the fourth speed-reverse clutch C4R is engaged, the rotation of the main shaft Sm is transmitted to the counter shaft Sc via the fourth speed-reverse clutch C4R, the first gear G1, the fifth gear G5 and the chamfer 56 so establishing a fourth speed gear shift stage.
When the fifth speed clutch C5 is engaged, the rotation of the main shaft Sm is transmitted to the counter shaft Sc via the fifth speed clutch C5, the second gear G2 and the sixth gear G6 so establishing a fifth speed gear shift stage.
When the counter reverse gear 54 is connected to the counter shaft Sc by means of the chamfer 56 in a state in which the fourth speed-reverse clutch C4R is engaged, the rotation of the main shaft Sm is transmitted as a reverse rotation to the counter shaft Sc via the fourth speed-reverse clutch C4R, the main reverse gear 51, the reverse idler gear 55, the counter reverse gear 54 and the chamfer 56 so establishing a reverse gear shift stage.
However, with regard to the conventional stepless transmission illustrated in FIG. 6, the third speed clutch C3 provided on the counter shaft Sc is placed on the end of the shaft opposite to the engine E, this third speed clutch C3 is not aligned with any of the other clutches in a direction perpendicular to the axial direction, and there is therefore the problem that the axial length of the automatic transmission increases by an amount corresponding to the distance the third speed clutch C3 projects in the axial direction.
The present invention has been carried out in view of the above-mentioned circumstances and it is an object of the present invention to reduce the axial length of the automatic transmission by efficiently arranging the gears and clutches used for establishing a plurality of gear shift stages.
In order to achieve the above-mentioned objective, in accordance with a first characteristic of the invention, there is proposed a four parallel shaft type automatic transmission comprising, in parallel, a main shaft, a counter shaft to which the rotation of the main shaft is directly transmitted via a first route, a first sub-shaft provided on a second route through which the rotation of the main shaft is transmitted to the counter shaft, and a second sub-shaft provided on a third route through which the rotation of the main shaft is transmitted to the counter shaft, wherein a first gear for transmitting the rotation of the main shaft to the counter shaft via the second route and a second gear for transmitting the rotation of the main shaft to the counter shaft via the first route are provided on the main shaft, a third gear and a fourth gear for transmitting the rotation of the main shaft to the counter shaft via the third route are provided on the second sub-shaft, the first gear and the third gear are provided within a first plane extending in a direction perpendicular to the shafts, and the second gear and the fourth gear are provided within a second plane extending in a direction perpendicular to the shafts.
In accordance with the above-mentioned arrangement, the first gear provided on the main shaft for transmitting the rotation of the main shaft to the counter shaft via the second route and the third gear provided on the second sub-shaft for transmitting the rotation of the main shaft to the counter shaft via the third route are provided within a first plane extending in a direction perpendicular to the shafts, and the second gear provided on the main shaft for transmitting the rotation of the main shaft to the counter shaft via the first route and the fourth gear supported on the second sub-shaft for transmitting the rotation of the main shaft to the counter shaft via the third route are provided within a second plane extending in a direction perpendicular to the shafts. Therefore, the first gear of the main shaft can be used for transmitting power via both the second route and the third route, and the second gear of the main shaft can be used for transmitting power via both the first route and the third route so reducing the number of gears and the axial length of the automatic transmission.
In accordance with a second characteristic of the invention, there is proposed a four parallel shaft type automatic transmission comprising, in parallel, a main shaft, a counter shaft to which the rotation of the main shaft is directly transmitted via a first route, a first sub-shaft provided on a second route through which the rotation of the main shaft is transmitted to the counter shaft, and a second sub-shaft provided on a third route through which the rotation of the main shaft is transmitted to the counter shaft, wherein a first gear for transmitting the rotation of the main shaft to the counter shaft via the second route and a second gear for transmitting the rotation of the main shaft to the counter shaft via the first route are provided on the main shaft, a third gear and a fourth gear for transmitting the rotation of the main shaft to the counter shaft via the third route are provided on the second sub-shaft, the first gear fixed to the main shaft is meshed with the third gear provided on the second sub-shaft in a manner such that the third gear can be freely engaged and disengaged, and the second gear provided on the main shaft in a manner such that the second gear can be freely engaged and disengaged is meshed with the fourth gear fixed on the second sub-shaft.
In accordance with the above-mentioned arrangement, in addition to the first characteristic of the invention, since the first gear fixed to the main shaft is meshed with the third gear provided on the second sub-shaft in a manner such that the third gear can be freely engaged and disengaged, and the second gear provided on the main shaft in a manner such that the second gear can be freely engaged and disengaged is meshed with the fourth gear fixed on the second sub-shaft, connecting the third gear to the second sub-shaft can establish a gear shift stage via the third route, and connecting the fourth gear to the main shaft can establish a gear shift stage via the first route.
In accordance with a third characteristic of the invention, in addition to the arrangement of the second characteristic, there is proposed a four parallel shaft type automatic transmission wherein the second gear provided on the main shaft in a manner such that the second gear can be freely engaged and disengaged is also used as an idler gear provided on the third route for transmitting the rotation of the main shaft to the counter shaft via the second sub-shaft.
In accordance with the above-mentioned arrangement, since the second gear provided on the main shaft in a manner such that the second gear can be freely engaged and disengaged is also used as an idler gear provided on the third route for transmitting the rotation of the main shaft to the counter shaft via the second sub-shaft, the number of gears can be further decreased so further reducing the axial length of the automatic transmission.
In accordance with a fourth characteristic of the invention, there is proposed a four parallel shaft type automatic transmission comprising, in parallel, a main shaft connected to an engine, a counter shaft connected to driven wheels, a first sub-shaft and a second sub-shaft to which the driving force of the main shaft is transmitted via a gear train, two low speed clutches for transmitting the rotation of the first sub-shaft to the counter shaft being provided on the first sub-shaft, a medium speed clutch for transmitting the rotation of the main shaft to the second sub-shaft being provided on the second sub-shaft, and high speed clutches for transmitting the rotation of the main shaft to the counter shaft being provided on the main shaft, wherein one of the low speed clutches and the high speed clutches are placed on one side of the gear train so that the low speed clutch and the high speed clutches are aligned with each other in a direction perpendicular to the shafts, and the other low speed clutch and the medium speed clutch are placed on the other side of the gear train so that the low speed clutch and the medium speed clutch are aligned with each other in a direction perpendicular to the shafts.
In accordance with the above-mentioned arrangement, the driving force of the main shaft is transmitted to the first sub-shaft and the second sub-shaft via the gear train, one of the two low speed clutches and the high speed clutches are placed on one side of the gear train so that the low speed clutch and the high speed clutches are aligned with each other in a direction perpendicular to the shafts, and the other low speed clutch and the medium speed clutch are placed on the other side of the gear train so that the low speed clutch and the medium speed clutch are aligned with each other in a direction perpendicular to the shafts. Therefore, the overall axial length of the low, medium and high speed clutches can be shortened so reducing the size of the automatic transmission.
In accordance with a fifth characteristic of the invention, in addition to the arrangement of the fourth characteristic, there is proposed a four parallel shaft type automatic transmission wherein a gear included in the gear train is placed on an almost central part of the first sub-shaft, the two ends of the first sub-shaft being supported by bearings, and a first speed gear for establishing a first speed gear shift stage and a second speed gear for establishing a second speed gear shift stage are placed on either side of the gear so as to adjoin it.
In accordance with the above-mentioned arrangement, when a first speed gear shift stage is established, the driving force is transmitted via the gear in the gear train placed on a substantially central part of the first sub-shaft, the two ends of the first sub-shaft being supported, and the first gear adjoining one side of the above-mentioned gear; when a second speed gear shift stage is established the driving force is transmitted via the gear in the above-mentioned gear train and the second gear adjoining the other side of the above-mentioned gear. Therefore, the curvature of the first sub-shaft accompanying the transmission of the driving force can be minimized so avoiding incomplete gear meshing and reducing the noise.
In accordance with a sixth characteristic of the invention, in addition to the arrangement of the fourth characteristic, there is proposed a four parallel shaft type automatic transmission wherein medium speed gears for transmitting the rotation of the second sub-shaft to the counter shaft by engagement of the medium speed clutch are also used as high speed gears for transmitting the rotation of the main shaft to the counter shaft by engagement of the high speed clutch.
In accordance with the above-mentioned arrangement, when the medium speed clutch is engaged, the rotation of the second sub-shaft is transmitted to the counter shaft via the medium speed gears, and when the high speed clutch is engaged, the rotation of the main shaft is transmitted to the counter shaft via the medium speed gears that are as the high speed gears. Therefore, the number of gears can be so contributing to a reduction in the size of the automatic transmission. The route for establishing the fourth speed gear shift stage, the fifth speed gear shift stage and the reverse gear shift stage in the embodiment corresponds to the first route in the present invention, the route for establishing the first speed gear shift stage and the second speed gear shift stage in the embodiment corresponds to the second route in the present invention, and the route for establishing the third speed gear shift stage in the embodiment corresponds to the third route in the present invention.
The sub-shaft drive first gear 31 in the embodiment corresponds to the first gear of the present invention, the main three speed-fourth speed gear 48 in the embodiment corresponds to the second gear of the present invention, the first sub second gear 43 in the embodiment corresponds to the third gear of the present invention, and the second sub third speed gear 46 in the embodiment corresponds to the fourth gear of the present invention.
The first speed clutch C1 and the second speed clutch C2 in the embodiment correspond to the low speed clutch of the present invention, the third speed clutch C3 in the embodiment corresponds to the medium speed clutch of the present invention, the fourth speed clutch C4 and the fifth speed-reverse clutch C5R in the embodiment correspond to high speed clutches of the present invention, the sub-shaft drive first gear 31 to the sub-shaft drive fourth gear 34 in the embodiment correspond to the gear train of the present invention, the first sub first speed gear 40 in the embodiment corresponds to the first speed gear of the present invention, the first sub second speed gear 43 in the embodiment corresponds to the second speed gear of the present invention, and the main third speed-fourth speed gear 48 and the counter third speed-fourth speed gear 52 in the embodiment correspond to the medium speed gear and the high speed gear of the present invention.